Growth Associated Protein-(GAP)-43 is an axonal protein expressed at elevated levels during periods of axonal growth and regeneration which appears to play a central role in these processes. Experiments outlined herein are directed towards analyzing the time-course and distribution of GAP-43, cloned into an expression vector, will be used to generate specific antisera. Immunocytochemical detention of GAP-43 in the developing nervous system will reveal when GAP-43 expression begins and hence whether this protein is involved in the early events of neurogenesis. Previous investigations have demonstrated that elevated expression of GAP-43 coincides with nerve growth factor (NGF)-induced neurite outgrowth from cultured PC12 pheochromocytoma cells. To assess the role of GAP-43 in NGF-induced neurite outgrowth, the cDNA for GAP- 43 under the control of an inducible promoter will be introduced into PC12 cells, thus permitting experimental modulation of the expression of this protein. These studies will reveal whether elevated expression of GAP-43 is sufficient or necessary for axonal outgrowth in this system. GAP-43 appears to be a member of a small group of proteins specifically involved in axonal growth and regeneration. Investigation of these proteins and the regulation of their expression may eventually permit us to promote axonal re-growth after injury to the nervous system.